(1) Field of the Invention
This invention relates to a process for treating rosin. More particularly, this invention relates to a process for treating tall oil rosin with a zinc catalyst and a boric acid catalyst to improve color and color stability of the tall oil rosin acids.
Tall oil is a natural mixture of rosin acids and fatty acids, together with unsaponifiable materials, which is obtained by acidifying the black liquor skimmings of the sulfate process of wood pulp manufacture, using resinous woods such as pine. The composition of tall oil varies somewhat depending upon such factors as the species of the wood which was pulped. Crude tall oil acids generally contain from about 18% to 60% fatty acids, 28% to 66% rosin acids and 3% to 24% other constituents, notably unsaponifiable materials. Crude tall oil may be distilled and fractioned to separate the fatty acid and rosin acid fractions.
Tall oil rosin consists of a major portion of resin acids which are monocarboxylic acids of alkyl hydrophenanthrene. The major resin acids found in tall oil rosin are abietic acid, dehydroabietic acid, neoabietic, palustric, pimaric acid, and isopimaric acid. Tall oil rosin usually contains a small amount of fatty acids as well as some unsaponifiable material.
(2) The Prior Art
In the processing of rosin at elevated temperatures, care must be taken to prevent the unwanted decarboxylation reaction, since this causes a decrease in both acid number and softening point and increases color. When rosin is heated to about 300.degree. C. (572.degree. F.) or higher, decarboxylation occurs with the formation of nearly neutral material known as rosin oil. Decarboxylation also takes place readily in the presence of catalysts, such as zinc, sulfonic acids and siliceous earths at temperatures of 120.degree. C.-280.degree. C. (248.degree. F.-536.degree. F.). The rate of decarboxylation is greatly increased by the use of these and other acidic catalysts. The color of rosin and its tendency to decarboxylate at high temperatures have hindered the desirability of their use in many applications where color is important. To attest this fact, the prior art is replete with methods for making rosin lighter in color with changing the character of the rosin. Treatment of rosin with zinc to make resinates is illustrated by U.S. Pat. No. 2,396,671 to Aver, U.S. Pat. No. 2,394,416 to Ziess, U.S. Pat. No. 3,912,709 to Gould, and U.S. Pat. No. 3,929,703 to Weyman. Zinc has also been used to improve color of fatty acids from which all or a major proportion of the rosin acids have been removed as shown by Nevin in U.S. Pat. No. 2,763,638.
Boric acid and borax are also known catalysts for treating fatty acids. For example, in U.S. Pat. No. 2,862,943 to Wheeler small amounts of boric acid were used to treat tall oil fatty acids to improve color; but if the fatty acids contained more than 1% rosin, decarboxylation becomes a problem. U.S. Pat. No. 2,448,621 to Rice and U.S. Pat. No. 2,441,063 to Gilmann teach treating fatty acid and rosin materials with boric acid or borax.
It is, therefore, the general object of this invention to provide a catalyst system for treating rosin to upgrade and stabilize its color.
Another object of this invention is to provide a process for upgrading the color and maintaining the color stability of tall oil rosin and at the same time improve acid number and softening point.
It is a further object of this invention to provide a process which accomplishes the above objects using in combination a zinc catalyst and boric acid catalyst.
Other objects, features and advantages of this invention will be evident from the following detailed description.